1. Field of the Invention
The present invention relates to a magnetic head slider unit for reading or writing data to/or from a magnetic medium, such as a magnetic disk and to a magnetic disk apparatus incorporating such a magnetic head slider unit.
2. Summary of the Prior Art
In order to read or write data to/or from a magnetic medium such as a magnetic disk, it has been proposed to mount a magnetic head on a slider, which slider is movable over the surface of the disk. The slider is shaped so as to form an air film between its surface adjacent the disk (hereinafter called the "float surface"), and the adjacent surface of the magnetic disk. That air film ensures that the slider maintains a distance of less than 1 micron, which distance is generally referred to as the "float distance" an example of such a magnetic head slider unit is disclosed in, for example, U.S. Pat. No. 3,823,416 (equivalent to JP-B-57-569).
Although the float distance is small, it is very important that the slider does not contact the disk itself while it is moving. If this were to happen, irrepairable damage could be caused to the disk.
In U.S. Pat. No. 3,823,416, the magnetic head is fixed to the trailing edge of the slider, and so must necessarily also remain clear of the surface of the magnetic disk when the slider is moving relative thereto.
JP-A-62-250570 proposes an arrangement in which the magnetic head is connected to the slider by a piezoelectric actuator, with the actuator being deformable under the influence of electric current to move the head relative to the slider. However, it can readily be appreciated that such an actuator cannot respond to very rapid changes in the float distance.
Although, magnetic disks are made so that their surfaces are as smooth as possible, there is inevitably some surface roughness of the disk surface, and there may be more substantial disk deformation caused by air movement. Such roughness and disk deformation imposes a practical limit on the permissible float distance between the slider and the disk. On the other hand, the spacing between the head and the disk affects the capacity of the apparatus to read and write data. In order to increase the capacity, it is desirable for the spacing between the head and the disk to be reduced, preferably to zero. If, however, the magnetic head of the slider unit disclosed in U.S. Pat. No. 3,823,416 or JP-A-62-250570 were to be brought into contact with the disk when the slider was moving relative to the disk, then the disk would be damaged. In order to compensate for, for example, surface roughness, the magnetic head must move, but in the arrangements of U.S. Pat. No. 3,823,416 and JP-A-62-250570, such movement has an inertia corresponding to the whole of the slider unit. Thus, rapid movement is not possible and the magnetic head will then cause a significant force to be applied to the disk when roughness is encountered.
U.S. Pat. No. 4,819,091 sought to achieve an arrangement in which the magnetic head was in contact with the disk and, for this purpose, the slider is dispensed with, and instead the magnetic head is formed as part of a single crystal. The single crystal has the advantage of high thermal conductivity, a low coefficient of friction and a high surface energy. The crystal could be, for example, the 110 crystal plane of diamond. However, it is believed that it is still not possible to make such a single crystal mounting for the magnetic head which will not cause damage to the disk if there is disk roughness.
Therefore, it is necessary to find some way of permitting the head to contact the surface of the disk, and yet allow that head to move to compensate for, for example, surface roughness of the disk without requiring the whole of the slider to move JP-A-63-306514 attempts to address this problem, and will be discussed in more detail later. An article in IEICE Technical Report Vol 89, No 29, MR89-4, published in Japanese by the Institute of Electronics, Information and Communication Engineers and partially republished in "Intermag 90", the 1990 Digests of the Intermay Conference in an article entitled "Recording Characteristics of Perpendicular Magnetic Rigid Disk Measured by Non-Flying Single-Pole Head" by Y. Nakamura et al, on paper FQ-05 will also be discussed. This article will be referred to as "Report MR89-4".